Fuel mixing and delivery system



April 20, 1954 J. A. HARRISON 2,675,820

FUEL MIXING AND DELIVERY SYSTEM l Filed Feb. l, 1 946- 3 Sheets-Sheet l April 20, 1954 J, A. HARRISON FUEL MIXING ND DELIVERY SYSTEM 5 Sheets-Sheet 2 Filed Feb. l, 1946 will w III m April 20, 1954 J. A. HARRISON 2,675,820

FUEL MIXING AND DELIVERY SYSTEM Filed Feb. l, 1946 3 Sheets-Sheet 3 James Harr/son WI/ad L Yeliminates the necessity of providing changeable parts of different sizes and the neces- Patented Apr. 20, 1954 UNITED STATES PATENT OFFICE James A. Harrison, Southfield Township, Oakland County, Mich.

Application February 1, 1946, Serial No. 644,755

13 Claims. l

This invention relates to a novel method of and apparatus for mixing and proportioning gases and air for producing and supplying a combustible fuel mixture and particularly to such a method and apparatus especially adapted for industrial use in gas red appliances.

Heretofore, gas mixing` and proportioning systems for gas red furnaces have been limited to a narrow range in the selection of the number and the size of burners and in the selection of the proper size of the proportional gas-air mixer to supply the burner selected. Frequently, after such equipment had been installed it was found necessary to send back for parts of different sizes to meet the particular operating condition. Most commercial equipment of this kind has been made with interchangeable parts of different sizes for just such purposes. One-commercial system, for example, provides some twenty different sizes of air jet and Venturi sleeve devices from which the purchaser is required to select the size which will operate most effectively. Another system has a removable machined Venturi insert for which diiierent sizes may be substituted to obtain the desired ring characteristics. A third system, for

area of the burner orifices. In the systems here- Y tofore used the maximum turn down ratio from full capacity to minimum capacity has been approximately 4 to l. This limited range plus the multiplicity of interchangeable parts of different sizes has made for relatively costly and ineiicient gas combustion systems in the past.

An important object of this invention is to provide an improved method of and apparatus for mixing, proportioning and supplying a combustible fuel mixture to gas fired furnaces which intersity of determining which of several 'interchangeable parts will obtain the maximum effectiveness. Another object of this invention is to provide such a method and system which fur'- nishes within the limits of the equipment any mixture pressure desired by the simple expedient of adjusting ene controlling device. Another object of this invention is to provide a fuel cornbustion vsystem for gas fired appliances which increases the range of the turn down ratio many times over that heretofore obtained. An important result of this invention is the ability to use a greater number of burners in the system to make up the total capacity and by means of valves or gas cocks to separately turn on or off the burners or operate them at any intermediate condition to suit an intricate heating cycle or to vary the heating operation oi one part of the furnace with respect to any other part. y

An important object of this invention is to provide a novel method of and apparatus for controlling the supply of combustible fuel wherein a constant pressure is maintained in the system and the orice of the burners are varied automatically depending upon the pressure of the gasair mixture supplied thereto. As a result, an innite turn-down ratio is available and the orince area of the burner or burners will always be just exactly equal to that necessary to pass the volume of mixture being supplied. Thus the system as a whole exhibits a constant pressure and one or more variable burner orifices automatically responsive to the pressure of the mixture in the system. v

More particularly, it is an important object of this invention to provide a gas and air mixing and proportioning device having an adjustable part which eliminates the pre-selection of one of many interchangeable parts heretofore used and which when adjusted will make available any mixture pressure within the limits of the system. The novel mixing and proportioning device of this invention includes a Venturi shaped tube having 'a hollow member or plug therein which is adjustable longitudinally to vary the mixing pressure and through which one oi. the constituents of the fuel mixture is'delivered. Novel control means is provided for adjusting this hollow member relative to the Venturi passage. In one form of the invention, a pressure responsive device automatically responsive to the air pressure delivered and the mixture pressure supplied is operable to adjusta movable hollow member or Venturi plug. In another form of the invention, electrical means which may be responsive to the temperature conditions in the furnace is operable to adjust the movable member. In a third form of the invention a manual control is operable to make the adjustment.

Various other objects, advantages and meritorious features will become more fully apparent from the following specification, appended claims and accompanying drawings, wherein:

Figure 1 is a view of a gas and air mixing and supply system embodying the invention partly broken away to illustate the internal construction of certain parts thereof,

Fig. 2 is an enlarged longitudinal cross section view of the gas and air mixing device of the system illustrated in Fig. 1,

Fig. 3 is a detail view of the gas admission port of the device of Fig. 2,

Fig. 4 isl a view of one end of the device of Fig. 2 modied for manual control,

Fig. 5 is a View of a modified form of control for the mixing device of Fig. 2 utilizing electrical means responsive to the temperature of the furnace for eifecting control.

The embodiment of the invention illustrated in Fig. 1 comprises a plurality of burners |02 dis'- posed in line along the outside of the furnace wall l2 and arranged to discharge burning gases through separate ports I4 associatedwith each burner. A manifold which may be of any suitable form supplies the combustiblev mixture to the burners. In the illustrated embodiment the manifold consists of a short superimposi-n-gpipe section IS having depending sections leading to two of the intermediate burners from which branch lines i8 run to the outer burners to supply the same with fuel. The manifold section IB connects through pipe. section with a gas and air proportional mixing device generally indicated at 22. The latter receives air from inlet pipe 23 leading from a blower 24 and gas from a gas main indicated at 2E.

The gas main 25 is providedl with a gas cock 28 for controlling the delivery of gas to the mixing device 22 and a gas pressure regulator 30 of standard construction. A temperature control valve 32 to which morek detail reference will be made hereinafter is installed in the pipe section 20 between the mixer and the burner. A thermocouple 34 in a protected tube 36 is inserted in the furnace wall and is electrically connected by means described hereinafter with the valve 32 for operating the same.

Three forms of the gas and air proportional mixing devices 22 constructed in accordance with this invention are illustrated herein, and they are generally similar except for the mode of control thereover. In the system of Fig. 1 an automatically self-regulating constant outlet pressure mixing device 22 is employed. It is provided with an enlarged headr 38 forming a housing for a pressure responsive diaphragm motor. The diaphragm housng communicates with the air inlet pipe 23 by means of an air delivery conduit 4!! vin which an air pressure regulator 42 is installed.

The air and gas mixing device is illustrated in detail in Fig. 2. It comprises generally an outer elongated stationary tubular body 44 formed of a plurality of sections threadedly or otherwise joined together in the manner shown in Fig. 2. To one end'of this body 44 is the housing 38 containing the diaphragm 46 therein. The tubular body 44 has a reduced or constricted section 48 intermediate its ends which is shaped to form a pair of adioining oppositely directed outwardly flaring wall portions. Mounted coaxially within the body 44 is an inner movable member 50 formed of several connected parts including a hollow sleeve portion 52 extending toward one end of the outer tube and a partially solid portion 54 having a conical or tapering exterior which as will be described hereinafter forms a Venturi plug cooperating with the inner wall surfaces of the outer tube 44 to form a Venturi passage. The inner member 50 has outside dimensions less than the inside dimension of the tube 44 to thereby form an annular passage therethrough.

As shown, the plug 54 gradually tapers toward its opposite ends from a maximum diameter intermediate its ends. One tapered end portion of the plug is disposed in opposed relation to one of the outwardly flaring wall portions of the constricted section 48 and has a length substantially equal thereto. So formed and disposed, the plug cooperates with the outwardly flaring wall portions of the constricted section 48 to define a Venturi passage having an upstream converging entrance and a downstream diverging exit connected by a throat of material axial dimension. In the position of the parts shown in Fig. 2, the throat has an axial dimension approximately equal to that of the outwardly flaring wall portion of the constricted section in which the plug lies. As the plug shifts axially of the tube, as hereinafter described, it will vary the cross. sectional area of the throat and thereby vary the volume of air passing through the throat.

It is noted in Fig. 2 that the conical surface of the plug 54 in the throat extends at a diverging angle to the surrounding outwardly haring wall of the constricted section 48 with the clearance between these two surfaces gradually increasing in the direction of minimum diameter of the constricted section. This gradual increase in clearance between these two sections is in inverse relation to the decrease in diameter of the outer tube and thereby results in a throat of approximately uniform cross section throughout its length in any set position of the plug'. Moreover. the inclination of these throat surfaces to the axis of the mixer will cause them to approach one another when the plug is axially shifted in one direction and to move away from one another when the plug is moved in the opposite direction thereby varying thev cross sectional area of the throat and the volume of the air constituent permitted to ow therethrough.

Ther two portions 52 and 54 of the inner member 50 are secured together for joint operation. The hollowed sleeve portion 52 is telescopingly slidingly received over a second inner sleeve 56 fixed to the end of the outer body 44. To the opposite end of the Venturi plug 54 is xed a coupling member 58. By means of any suitable dismountable connection a hollowed rod 60 is attached to the coupling member and forms an operating extension thereto. This connection may be in the form of a cylindrical member 62 press fitted into the end of the rod 60 and attached by means of pin 64 to the coupling membei" 58. Thev outer end of the hollow rod is connected by means of opposed plates 66--66 to the diaphragm 46. The various parts of the inner member 50 are connected together for joint movement, and in response to the exing of the diaphragm all these parts will reciprocate together relative to the outer tube 44. The telescoping connection of the sleeve portion 52 over the fixed sleeve 5B serves as one support for the inner Venturi plug member 50. An antifriction bearing 68 through which the hollowed rod B0 slides serves as a second support for the Venturi plug member.

The air inlet into the mixer 22 is indicated at 'l0 and communicates with the air delivery pipe 23. The gas inlet is designated at 12 and communicates with the gas delivery conduit 26. Both inlets are on one side of the Venturi pasvaried by the pressure regulating valve 42.

sage. The discharge outlet of the mixed gas and air is indicated at 14 on the opposite side of the Venturi passage. Air entering inlet travels through the annular passage of the tube 44 including the Venturi passage and ultimately discharges from the tube through theY outlet '14. Gas entering the inlet l2 is admitted through a rvariable slot shown in Fig. 3 into the hollowed portion 52 of the inner member and discharges therefrom into the Venturi passage through a series of annularly spaced ports 16 where it mixes with the air passing therethrough.

Referring to Fig. 3, there is mounted within the xed sleeve 56 over which the hollowed portion 52 of the inner member telescopes a third sleeve 18 which is rotatably adjustable. Both sleeves56 and 'I8 are provided with longitudinal slots which substantially register with one another to form the admission port 80 through which the gas enters the hollow interior of member 50, but by virtue of the rotatable adjustable character of sleeve 18 the port can be varied to alter the volume of gas admitted. The adjustment of the inner 'sleeve 'I8 would be made, if at all, only occasionally and depending upon the quality of the gas. At the time of installation of the equipment. tests would be run and the desired setting made at that time. In the illustrated equipment, the innermost sleeve 18 is held in adjusted position by the set screw 84 and access is gained thereto by removable cap 82. During operation of the system, movement of the Venturi plug member 50 will cause the outermost sleeve 52 to slide over the slotted port 80 and increase or decrease its area depending upon the direction of movement of the Venturi plug.

In order to prevent the escape of gas and air from the areas where they are confined before and after intermixture. any suitable form of seals may be used. As shown, a bellows type of seal 86 prevents the intermingling of gas and air at their respective inlet areas. A similar type of seal 88 prevents the escape of the fuel mixture into the diaphragm housing.

The rod 60 is hollowed as previously mentioned for the purpose of establishing communication between the gaseous fuel mixture at the discharge outlet 'I4 and one side of the diaphragm 46 which in this instance is the outboard side. This is accomplished by the provision of one or more bleeder holes 90 on the inner end of rod 60. The opposite end of the hollowed rod extends beyond the diaphragm and its supporting plates 66--66 and opens out into the area on the outboard side of the diaphragm. There is thus established a yielding force on one side of the diaphragm opposing the pressure of air admitted to the other side through conduit 40. As previously described, the latter is connected to the air inlet pipe 23 and the amount of air permitted to enter the diaphragm housing is A control member which :may be in the form of an adjustable screw 92 is provided for regulating the valve. Air admitted to the underside of the diaphragm motor is permitted to escape through the bleeder port 94. The amount of air pressure admitted to the inboard side of the diaphragm controls the movement of the Venturi plug member 50 and thereby governs the amount of mixture outlet pressure.

Fimctioning automatically as previously described are the burner devices I0. Each burner device has an elongated body closed at its outer end and opening at its inner end into one of 6 the ports |4 of the furnace wall. The body includes a nozzle portion |02 threadedly engaged in a mounting ange |04 secured to the outer surface of the furnace wall. The fuel mixture delivery pipe I8 communicates with each burner I0 and opens into its body intermediate its opposite ends. Axially reciprocal in each burner is a cone shaped plug ||6 which is positioned in the nozzle and cooperates 'with the inner wall of the latter to vary the nozzle opening. The plug is carried on the extremity of a rod ||8. The latter is yieldingly constrained by an adjustable coiled spring |20 to move the plug in the direction to close the nozzle opening. The plug is provided with an axial passage opened at both ends which serves as a duct for delivering a small quantity of gas mixture for a pilot light.

By the use of the movable oriiice plug ||=E and the adjustable spring |20, an infinite turn down ratio is available. The spring pressure would be set to equal the maximum pressure and in normal operation the pressure of the mixture admitted to the burner through the inlet pipe |'8 would be suilicient to force the plug outwardly against the tension of the spring and allow the fuel mixture to ow in ignited condition into the furnace port |4. As the supply of mixture to the burner is reduced in volume the orifice plug will move inwardly and eventually if the pressure falls low enough close the burner down with the exception of the pilot light. 'I'hus the orifice area of the burner would be just exactly equal to that necessary to pass the volume of mixture being supplied. A constant manifold pressure and an infinite turn down ratio is the result. The adjustable spring tension has the further advantage in that Where a number of burners are manifolded together as illustrated herein, each burner can be set independently of the others to close at any predetermined pressure and thus provide zone control or zones of different temperatures in the furnace. Moreover. each vburner unit may be provided with a valve immediately adjacent thereto for cutting off the delivery of fuel thereto.

The temperature control valve 32 in the line from the mixer 22 to the burner manifold is electrically controlled by a motor housed in the unit |40 attached to the pipe line 20 and by means of the leverage connection |42 is capable of swinging the valve 32 to various positions to change the volume of fuel mixture delivered to the manifold. An electrical control instrument generally indicated at |44 is electrically coupled with the valve control motor by leads |46 and with the thermo-couple 34 by leads |48, and in response to the latter closes electrical contacts in the valve motor circuit which shifts the valve 32 to various positions, which in this particular embodiment of the invention is either high, 10W or closed Any other intermediate positions of the valve may be included in the control if desired.

Viewing the system of Fig. 1 as a whole, there is provided a self-balancing proportional air and gas mixing device 22 delivering a fuel mixture under a preset constant pressure to a plurality of automatic pressure responsive burners 0, each of which may be independently set to automatically close at diierent pressures. The inner Venturi plug member 50 of the mixing device is controlled by the air pressure operated diaphragm 4B. Due to the characteristics of this novel type of mixer, if four ounces of air pressure is imposed on the inboard lside of the diaphragm 46 a four vounce burner mixture will result, regardless of the size and number of burners being' supplied.

a sixv ounce air pressure is imposed, a six ounce yburner mixture willl result, and so on up to eight, nine, ten or higher ounce pressures depending upon the maximum pressures available in the combustion air. The selection of the mixture pressure is: determined by the setting of the pilot pressure regulator 42 in the air line 40 leading to the inboard side of the diaphragm.

In commencing the operation of the system, if eight ounces of mixture pressure is desired and 'the pressure regulator 42 is adjusted to this amount, the immediatek delivery of this pressure to the inboard side of the diaphragm 46' by way ci tube d will causek the latter to move outwardly to a position approximately that shown in full lines in Fig. 2. As the pressure of the gas-air mixture builds up in the burner manifold a condition will be reached when this pressure equals that imposed on the inboard side of the diaphragm. This mixture pressure, as previously explained, is conveyed to the outer or outboard side of the diaphragm by way of the ports 91Ev and the hollow interior of the rod 60. If this gas-air mixture pressure should go above that imposed on the inboard side of the diaphragm, the latter will be caused to be moved inwardly because of the higher diierential pres sure on its outboard side, `This inward movement of the diaphragm will carry the Venturi plug closer to the Walls of the Venturi passage and reduce the volume of air passing therethrough and reduce the outgoing gas-air mixture delivered to the burners. Thus it is apparent that the diaphragm will automatically take a position which equalizes the pressure of the gasair mixture with the pressure or force imposed on its inboard side. If the pressure regulator 42 is now adjusted for twelve ounce mixture pressure, the increase in pressure on the inboard side of the diaphragm will move this element and the Venturi plug to the right in Fig. 2 and permit more air to pass through the Venturi passage. The increase in gas-air mixture which will re- -sult will very quickly stabilize the diaphragm at a position where the outgoing mixture pressure equals that imposed on the inboard side of the diaphragm.

The air pressure utilized for controlling the diaphragm motor is taken for reasons of economy from the combustion air blower line 23. However, air pressure from a separate source may be used if desired. In place of the air pressure on the inboard side of the diaphragm, other force applying means may be used, such as a spring. These alternatives are suggested to show that the system is not confined to that illustrated but is capable of modification within the principles of the invention.

A particular advantage derived from this selfbalancing type of system is that valve means may be installed at any point in the system beyond the mixing device, such as the temperature control valve 32, the automatic pressure responsive valves in the burners la, and the cut-01T valves |48. The latter may be adjusted while in use to completely cut oi the operation of one or more burners without effecting the system as a Whole in order to meet the varying heat demands of the appliance. It has been determined that the ratio of turn down with this self-balancing type of mixer is many times that heretofore obtained and one such test indicated a turn down ratio for this invention of 13 to 1. If desired, automatic temperature control; valves may be installed on each burner, or group of burners', all deriving their gaseous fuel mixture from a single selfbalancing type of air and gas mixing device of the ltype illustrated and described herein.

The self-balancing diaphragm operated mixing device of Fig. 2 illustrates one form of the invention. Other means for shifting the inner Venturi plug member 5G may be employed and in Fig. 4 a novel manual control is shown. The air and gas mixing device is similar to that shown in Fig. 2 except for the change at the discharge end thereof where the manual control is substituted for the diaphragm motor. The outer body 45 which is generally similar to the outer member 4d of Fig. 2 has a fuel mixture discharge outlet 15 similar to 'M of Fig, 2. The inner movable Venturi plug member 5| is similar inv construction to member 5U of Fig. 2 except for the connection of an externally threaded rod 6| in place of the hollow rod 6D of Fig. 2. This rod is threadedly received in a closure member 63 secured to the end of the outer body 45. It is apparent that upon rotation of the rod it will be advanced or retracted longitudinally relative to the closure member and by virtue of its connection to the inner Venturi plug member cause the latter to rotate therein and simultaneously be adjusted longitudinally within the outer member to vary the size of the Venturi passage. The end of rod Si is squared at 65 to receive a wrench or other tool for turning, and a locknut B1 holds the rod in adjusted position. The operating end of the rod is enclosed in a removable cap 69.

In Fig. 5 an automatic electric control is shown for bodily shifting the Venturi plug member oi' the mixing device. The latter is similar in all respects to the device 22 of Fig. 2 except that in place of the diaphragm housing on the end of the device, a supporting plate 1| carries an electric motor housing 'I3 in which, as well understood by those skilled in the art, there is a reversible electric motor operatively connected to the shaft l5 for rotating it in either direction. A linkage system consisting of slotted members TI, I9 and 8| operatively connects the exposed end of rod 6i] with the shaft 15. The latter includes a pin 33 on the end of the rod which is slidable along the slot of linky 19 as the latter shifts and swings in response to the oscillation of the link TI.

The electric motor in the housing 'i3 is con- `nected by leads to a switch control generally vand as is apparent from the linkage connection either advances or retracts the rod 50 and the Venturi plug to which it is attached,` This will automatically vary the amount of gas-air mixture supplied to the burners 93.

What I claim is:

l. A gas and air mixing device for gas fired furnaces and the like comprising, in combination, a tube having a section thereof intermediate its ends constricted to form a Venturi passage, a hollow member cio-axially arranged in said tube in spaced relation to the walls thereof extending beyond said Venturi passage on either side thereof, means mounting said member for longitudinal movement in said tube, control means 9 operable on one end of said member for effecting longitudinal movement thereof, means for introducing air under pressure into said tube and thereby cause the same to flow through said Venturi passage, means for introducing gas into said hollow member adjacent the end thereof opposite to that operated upon by said control means, means for discharging said gas from said member into said Venturi passage, means responsive to the longitudinal movement of said member for varying the cross sectional area of said Venturi passage, and means responsive to the longitudinal movement of said hollow member for varying the amount of gas introduced into the member.

2. A gas and air mixing device comprising, in combination, a tube having a section intermediate its ends shaped to form a Venturi passage, a hollow member mounted co-axially in said tube in spaced relation to the Walls thereof and extending through said Venturi passage and beyond either side thereof to adjacent the ends of the tube, means for introducing air under pressure into said tube on one side of said Venturi passage and for discharging said air from said tube on the other side of the Venturi passage, a sleeve fixed in one end of said tube and telescopingly mounted with respect to one end of vsaid hollow member, said sleeve having an opening through the side thereof adjacent said end of the hollow member, means for introducing gas into said opening into said sleeve and thereby cause same to flow into said hollow member, means for discharging the gas thus introduced into said member into said Venturi passage for mixture with the air passing therethrough, means mounting said member for longitudinal movement in said tube, control means operable upon the end of said member opposite to that engaged by said sleeve for effecting longitudinal movement of the member, ythe telescoping connection of said sleeve and said member varying the gas inlet opening in the former proportionally to the longitudinal movement of the member, and means carried by said member cooperating with the walls of said Venturi passage and varying the area thereof upon longitudinal movement of the member.

3. A gas and air mixing device comprising, in combination, a tube having a Venturi passage and an inlet on one side of the Venturi passage and an outlet on the other side of the Venturi passage, a hollow member coaxially mounted in said tube in spaced relation to the walls thereof and provided with an inlet removed from said Venturi passage and one or more discharge ports opening into the Venturi passage, means for introducing air under pressure into said tube inlet to ow through the tube around said member and discharge therefrom through said tube outlet, means for introducing gas into said member inlet to flow through the member and discharge therefrom through said one or more ports into said Venturi passage where it is mixed with the air flowing therethrough, means mounting said member for 'longitudinal movement in said tube, means for varying the cross-sectional area of said Venturi passage proportional to said movement, pressure responsive means connected to said member for effecting movement of said member, and means counterbalancing said pressure responsive means between the pressure of the air introduced into said tube and the pressure of the air and gas mixture discharged from said outlet of the tube.

4. A gas and air mixing device comprising, in combination, a tube having a Venturi passage and an inlet on one side of the Venturi passage and an outlet on the other side of the Venturi passage, a hollow member coaxially mounted insaid tube in spaced relation to the walls thereof and provided with an inlet port removed from said Venturi passage and one or more discharge portsopening into the Venturi passage, means for introducing air under pressure into said tube inlet port to flow through the tube around said member and discharge therefrom through said tube outlet, means for introducing gas into said member inlet to flow through the member and discharge therefrom through said one or more discharge ports into said Venturi passage where it is mixed with the air flowing therethrough, means mounting said member for longitudinal movement in said tube, means for varying the cross-sectional area of said Venturi passage proportional to said longitudinal movement, a diaphragm in a closed housing operatively connected to said member for effecting longitudinal movement thereof, means for exerting a yielding force against one side of said diaphragm, and means providing communication between the opposite side of said diaphragm and the tube adjacent to said outlet and rendering said diaphragm responsive to the pressure of the gas and air mixture discharged through the outlet.

5. A gas and air mixing device comprising, in combination, a tube having a section of the inner wall thereof intermediate its ends constricted to form a Venturi passage having an axially elongated frusto-conically shaped throat portion, a hollow member co-axially` arranged in said tube in spaced relationjto the inner wall thereof and extending through said Venturi passage 'and beyond either end thereof, means mounting said hollow member for longitudinal movement in the tube, a cone shaped plu-g carried by said hollow member intermediate its ends and positioned in said throat portion of the Venturi passage and normally in spaced relation to the wall thereof, said cone shaped plug having an axial dimension approximating that of the throatportion of the Venturi passage, said tube having an air inlet on one side of the Venturi passage and an air outlet on the other side of the Venturi passage, means for introducing air under pressure into said inlet for flow through the Venturi passage of the `tube and for discharge from the tube through said outlet, said hollow member having a gas inlet remote from said Venturi passage and aY gas outlet through said lconical shapedV plug and into substantially the downstream end of the throat portionA of the Venturi passage, meansfor introducing gas into said gas inlet for ow through the hollow member and for discharge therefrom through said gas outlet into the Venturi passage, and control means operatively connected to the hollow member for effecting longii tudinal adjustment thereof and for varying the cross sectional area of the throat portionof the Venturi passage.

6. The invention describedinvclaim characu and for causing the member to move longitudinally in response to such rotation, and that the control means is operable to rotate the hollow member to eiect such longitudinal movement.

8. The invention described in claim 1 charactei-ized in that said control means constitutes a iiuid motor mounted on the end of the tube and operatively connected to the hollow member to eiect longitudinal movement thereof in the tube.

9. The invention described in claim 1 characterized in that said control means constitutes an electric motor mounted on the end of the tube and operatively connected to the hollow member to effect longitudinal movement thereof in the tube upon operation of the motor.

10. The invention described in claim 1 characterized in that said control means constitutes a threaded connection between the hollow member and the tube and arranged so that upon rotation of the member it will effect longitudinal movement of the member in the tube.

11. A gas and air mixing device for gas fired apparatus comprising, in combination, an outer tubular member, an inner tubular member coaxially mounted in the outer member in spaced relation to the walls thereof, said tubular members being shaped intermediate their ends to form a Venturi passagehaving an upstream converging entrance and a downstream diverging exit connected by a throat of material length, means for introducing uid forming. one constituent of the ultimate gas and air mixture into the outer member on the entrance side of said Venturi passage and for causing the same to ow through the space between said members and through the Venturi passage, said inner member having an axial conduit having a fluid inlet remote from said Venturi passage and a fluid outlet opening into the Venturi passage at substantially the downstream end of said throat, means for introducing another uid forming the second constituent of the ultimate gas and air mixture into said inlet of the inner member and thereby :causing the same to flow therethrough and discharge into the downstream end of the throat of the Venturi passage, means providing axial movement of one member relative to the other member, said axial movement varying the cross sectional area of the throat, and valve means associated with the fluid inlet of the inner member and responsive to the movement of said movable member for varying the amount of fluid entering the inlet.

12. In a gas and air mixing device for gas iired apparatus, a tube having the interior thereof intermediate its ends constricted to form adjoining communicating oppositely directed outwardly flaring wall portions, means for introducing one constituent of an ultimate gas and air mixture into the tube for now through the constricted area thereof, a member coaxially disposed in said tube in spaced relation to the walls thereof, a conical-shaped plug :carried on said member in opposed spaced relation to one of said outwardly iiaring wall portions and cooperating therewith and with the other outwardly flaring wall portion to form a Venturi passage having a converging upstream entrance and a diverging downstream exit connected by a throat of material length, said member being interi orly shaped to provide a longitudinal conduit having an outlet opening into substantially the downstream end of said throat, means for introducing the other constituent of the ultimate gas and air mixture into said conduit for iiow therethrough and for discharge from said outlet into the downstream end of the throat where it mixes with the first mentioned constituent to form the gas and air mixture, means mounting the member for axial shiftable movement, and control means for shifting the member, said plug moving in response to the axial shiftable movement of the member to vary the cross section area of the throat of said Venturi passage.

13. A gas and air mixing device for gas fired apparatus comprising, in combination, a tube having a section of its length constricted interiorly to form a communicating pair of oppositely directed outwardly flaring wall portions, a hollow member coaxially arranged in said tube in spaced relation to the walls thereof and extending through said constricted Section and having its opposite ends projecting beyond the outwardly flaring Wall portions thereof, means for introducing air under pressure into said tube at a point removed from said constricted section and for causing the air to flow through the tube and through the annular space between the flaring wall portions of the tube and the outer surfaces of the member, a cone shaped element carried by the member and disposed opposite one of said flaring wall portions with the slope of the element and the flaring wal* inclining generally in the same direction, said cone element together with the flaring wall portions forming a Venturi passage having an upstream converging entrance and a downstream diverging exit connected together by a communicating throat of material length, means for introducing gas into one projecting end of said hollow member, means for discharging the gas thus introduced from the cone shaped element into the downstream end of said throat of the Venturi passage, means mounting said member for longitudinal movement in said tube, and control means operatively engaging a projecting end of said member for adjusting the position of the member in the tube, said cone shaped element being responsive to such longitudinal movement of the member to vary the cross sectional area of said throat.

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